In the field of precision measurement, a grating ruler is often used as a displacement feedback apparatus, and the grating ruler utilizes a grating optical principle to measure a displacement or an angle precisely.
The existing grating ruler mainly includes two types, i.e., an incremental grating ruler and an absolute grating ruler, wherein the incremental grating ruler intervenes with an indicator grating through transmission or reflection depending on uniform scale lines irradiated by a light source to a glass or metal surface to generate alternately dark and bright moire fringes, and a moving distance is counted by counting the number of the fringes. The moire fringes can be subdivided according to requirements of measurement precision. Since a number of a simulation signal is subdivided, the signal is susceptible to the interference of an external environment and the detection precision is reduced. Moreover, when a resolution ratio is high, “step loss” may occur in a case of high-speed movement. The absolute grating ruler has a series of scribed lines with location coding information on a main grating ruler, thereby directly obtaining an absolute location and avoiding the “step loss” phenomenon, but a great amount of location coding information needs to be read, so that the processing speed is relatively low. Furthermore, the absolute grating ruler has high manufacturing requirements and high cost.
In general, no matter what way mentioned above is adopted, after the resolution ratio is increased, the feedback frequency is increased at a same speed; and due to the limitation of a highest cut-off frequency of an acquisition card, the resolution ratio is increased and the measurement speed is inevitably decreased.
Meanwhile, in order to improve the measurement precision, denser grating lines are needed, but the denser grating lines may lead to the increase of an acquisition amount of unit displacement data, causing that the “step loss” phenomenon occurs, the credibility of the data is reduced, and the “step loss” phenomenon is more apparent particularly at, a high-speed movement, state. In addition, by adopting a device with higher acquisition speed, the cost may be greatly increased. Therefore, high speed, high resolution ratio and high precision are intrinsic contradictions of the precision measurement of the grating.
The above-mentioned problems bring a challenge for high-speed and high-precision displacement positioning of electronic manufacturing equipment and need to be solved.